<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>CSS定位2</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
        body {
            height:700px;
        }

        header {
            position:fixed;
            width:100%;
            height:15%;
            top:0;
            right:0;
            left:0;
            bottom:auto;
            border: medium dashed #000000;
            background-color:#780000;
        }

        aside {
            position: fixed;
            width:5em;
            height:auto;
            top:15%;
            right:auto;
            left:0;
            bottom:100px;
            border: medium dashed #000000;
            background-color:#085144;
        }
        
        section {
            position: fixed;
            width:auto;
            height:auto;
            top:15%;
            right:0;
            left:5em;
            bottom:100px;
            border: medium dashed #000000;
            background-color:#025b95;
        }
        
        footer {
            position: fixed;
            width:100%;
            height:100px;
            top:auto;
            right:0;
            left:0;
            bottom:0;
            border: medium dashed #000000;
            background-color:#F4881a;
        }
    </style>
</head>
<body>
    <header>header</header>
    <aside>aside</aside>
    <section>section</section>
    <footer>footer</footer>
</body>
</html>